Ultrafast Micromachining: High-Quality Flexible Printed Circuit Processing with UV Picosecond Lasers

June 19, 2024

Ultrashort pulse (USP) lasers are increasingly being used in industrial manufacturing, with key applications in glass processing, metal




and medical device manufacturing. Short pulse widths in the infrared (IR) wavelength range of ~1µm enable high-quality processing with


minimal thermal effects, resulting in minimal melting and burring in metals and less chipping and cracking in glass compared to longer


nanosecond and microsecond pulse widths.


However, in many cases, shorter ultraviolet (UV) wavelengths offer additional benefits. Shorter wavelengths allow for smaller, more focused


spots and longer depths of field. In addition, UV wavelengths couple laser energy into a wider variety of materials than IR wavelengths. One


industry that combines many different materials is flexible printed circuit (FPC) manufacturing. FPCs are already used in a variety of compact


electronic devices, such as smartphones, watches, and a growing number of “wearable” electronics. Materials vary, including copper,


polymers, adhesives, and even paper. Common processes include drilling and contour cutting.


For FPCs, polyimide overcoats perform the same function as solder masks for FR4-based printed circuit boards (PCBs). Polyimide is typically


12–25 µm thick, coated with a pressure-sensitive adhesive, and bonded to a paper-based material. The key challenge is to ablate the pattern


in the polyimide at high speed while avoiding thermal effects such as melting of the adhesive and burning or charging of the paper base. The


current state-of-the-art overcoat patterning process combines pulsed nanosecond UV lasers with 2D galvanometers to achieve high-speed


processing with very low thermal effects. However, in some applications, quality is critical, so UV picosecond pulse widths are more




Compared to using nanosecond UV lasers, using picosecond UV lasers produces less debris while being able to process at higher pulse


frequencies (and thus at higher speeds) and does not cause unnecessary thermal effects in the adhesive and paper base.


With shorter pulse widths and shorter wavelengths, laser processing tends to produce higher quality, as shown here in the various FPC


processing results. Shorter interaction times and shallower light penetration depths allow for finer control of the ablation process, achieving


finer machining precision while reducing thermal effects.